Oncogene-associated transformation of rodent fibroblasts is accompanied by large morphologic and metabolic alterations

Cellular growth, proliferative activity, cell volume and metabolism of four differently transformed cell lines were investigated. Studies were carried out with spontaneously immortalized and poorly tumorigenic Rat1 cells, c-mycl-transfected and non-tumorigenic M1 fibroblasts, as well as their T24Ha-ras-(co)-transfected counterparts Rat1-T1 and MR1. Ras-transfection of both Rat1 and M1 cells, which is associated with aggressive tumor growth in vivo, caused significant morphological alterations, namely a 30-50% decrease in cell volume. A negative linear correlation between cell number and cell volume at confluence was observed. Furthermore, the expected stimulation of cellular growth rate after T24Ha-rastransfection was documented. Growth inhibition in Rat1 and M1 cultures was reflected by a dramatic decrease in the [H-3]thymidine labeling index (TLI) to below 3% while entering the stationary growth phase. In contrast, Rat1-T1 and MR1 cells had a TLI of greater than or equal to 18% even at confluence. Glucose uptake and lactate production were not different on a per cell basis: between parental cell line and the T24Ha-ras-transfected transformants. However, when these parameters were normalized for differences in cell volume, ras-transfection-resulted in increased glucose consumption and lactate release. The behavior of cellular and cell volume-related oxygen uptake throughout the growth period examined was remarkably different between the parental lines and the ras-transformed descendants. Oxygen consumption rates (QO(2)) of Rat1-T1 and MR1 cells were significantly less than those of Rat1 and M1 fibroblasts and showed different changes as a function of time in monolayer culture. Whereas the cellular QO(2) of the highly tumorigenic cell clones either decreased or leveled off throughout the entire period of plateau phase, a decline in cellular oxygen uptake was observed in the partly transformed cells until days 4-5 only. The decline was then followed by an increase with values almost returning to those recorded during the early exponential phase. The data presented demonstrate for the first time an impact of well-defined oncogenic alterations on the metabolic characteristics of cells which is a further step in the understanding of the pathophysiology of ras-associated tumor cells.